This invention relates to a method and apparatus for machining holes in crankshafts, and more particularly, for machining holes in crankshafts on a production scale basis.
Currently, crankshafts for automobile engines, truck engines or the like are manufactured and machined in large production quantities on a multi-station transfer line, each station of which is dedicated to machining one or more holes, such as oil holes, in the crankshafts. The transfer line works relatively well in that the same crankshaft for a given production model will have identically located oil holes for thousands and thousands of crankshafts which are machined. A particular problem is that the transfer line does not lend itself to changes in engine design where it is desirable to change the engine stroke thereby changing the particular angular position and location of the oil holes in the crankshafts relative to the crankshaft axis. The transfer lines are very long, expensive and time-consuming to build and install. Large and expensive fixtures must be built and be precisely positioned at each of the transfer stations, each of which has a machine head with a hole machining tool or tools. The ability to modify engines or to change the angle and the location of the crankshaft oil holes is a limitation that is difficult to overcome when machining oil holes in a transfer line.
It will be appreciated that such transfer lines are not well adapted to handle various sizes and shapes of crankshafts as well as to more modest changes in the same crankshaft. Additionally, the oil holes may be anywhere along and across the axial length of the crankshaft and at different rotational positions about the circumference of the crankshaft. Thus, dedicated transfer lines do not provide the desired flexibility with respect to adapting to very significant changes in position and angle of the cutting tool with respect to the crank""s longitudinal axis as well as to a rotational position about the circumference of the crankshaft.
On the other hand, the typical or standard cutting machine with three axes of movement is also not well suited for machining crankshafts. In such three axis machines the cutting tool is normally plunged along a given axis, vertical or horizontal. If the cutting tool for drilling of the oil holes is moved horizontally along an X or plunging axis, then it is also standard three-axis machine are able to move vertically in a Y direction normal to the horizontal plunge axis to change the height or the location of the hole along the longitudinal length of the crankshaft. The movement in the third orthogonal plane is usually or may be called a Z axis and would be a movement in the horizontal plane normal to the plunging axis. However, such machines can not readily machine oil holes anywhere along the length of the crank and at any angle through the crankshaft.
Thus, there is a need for a new and more flexible apparatus for machining oil holes in crankshafts.
In accordance with the present invention, an apparatus and method are provided in which a crankshaft is rotated about its longitudinal axis and is tilted relative to a fixed plunging axis of a cutting tool to machine oil holes at various positions and angles through the crankshaft. The cutting tool may also be moved along and across the length of the crankshaft to cut a hole anywhere along and across the axial length of the crankshaft. This is achieved by having the cutting tool travel along a fixed axis, and by mounting the crankshaft in a workholder or fixture in which the workholder and crankshaft tilt or pivot relative to the plunging axis of the cutting tool; and in which the crankshaft is spun about its longitudinal axis to the peripheral location for entry of the cutting tool. To provide oil holes anywhere along and across the axial extent of the crankshaft, the cutting tool may be moved in directions normal to the tool""s plunge axis. Thus, in the preferred embodiment of the invention, the crankshaft is mounted in a fixture or workholder; and the fixture is pivoted to change the angle of the crankshaft to the plunging axis and the crankshaft is spun about its longitudinal axis to allow entry of the tool anywhere about the circumference of the crankshaft. To locate the hole position along and across the axial length of the crankshaft, the tool head is shifted vertically and horizontally relative to the crankshaft.
In accordance with the present invention, the position and angle of the oil holes may be changed by controlling the software electronic controls which control the rotational spin axis location, the degree of tilt of the crankshaft, and the location of the plunge axis relative to the length and breadth of the crankshaft.
It is preferred that the fixture or workholder have a headstock and a tailstock therein for rotatably mounting the crankshaft, and also have an open face on one side thereof to permit loading or unloading of a crankshaft through the open face.
In accordance with one aspect of the invention, a bushing for guiding the cutting tool into the crankshaft is positioned relative to the crankshaft and the cutting tool by a bushing support. The bushing support utilizes a feed mechanism to advance and to retract the bushing relative to the crankshaft and to maintain the bushing in correct relative position independent of the plunge axis during machining of holes.
In accordance with an important aspect of the invention, the machine is particularly adaptable for machining different crankshafts in that it uses different cutting tools and supporting bushings therefor from an inventory of tools and bushings carried in an automatic storage and dispensing device, such as wine rack which stores tools and bushings for each of the particular hole configurations. That is, the machine tool is able to select different tools and bushings for each of the particular hole configurations for a given crankshaft; and of course, if a different size, shape or type of crankshaft is used, the inventory of bushings and cutting tools may be changed to provide the appropriate tools for the different crankshafts.
Preferably, an automatic toolchanger is mounted at a position remote from the machining head; and the fixture is titled to enlarge a space between it and the machine head. The tool changer is then shifted into this enlarged space between the fixture and the tool head, and then the tooling is changed and the tool changer is returned to its remote position.
In accordance with another important aspect of the invention, the production capability of the apparatus is increased by mounting a plurality of crankshafts side by side in a tiltable and rotatable fixture so that multiple crankshafts are machined simultaneously by multiple tools traveling along parallel plunging axes. This provides for the increased production from a single machine.
Thus, it will be seen that the present invention is particularly directed to the use of flexible software and to machine control technology to rapidly spin and tilt the crankshafts and to shift the cutting tool to each of the various positions needed for the oil holes.
The preferred crankshaft machine is a seven axis machine with a pair of crankshafts being mounted in a fixture that pivots about a centrally located pivot axis or trunnions relative to a fixed plane containing the plunging axis, with the crankshafts being rotated or spun in the fixture about their respective axial axes. The pair of cutting tools are mounted to move in a first plunging direction which direction is normal to the directions in which the tool head shifts relative to the crankshaft""s length and breadth to position the holes anywhere along and across the lengths of the crankshafts and at any angle to the axes of the crankshafts. It is much quicker and easier to be able to change the control and signal positions than to physically change dedicated transfer line equipment.